This invention relates to a water pump which is applied to an engine cooling system for a vehicle, and which is arranged to circulate a coolant water in the engine cooing system.
A Japanese Patent Application Publication No. 2004-176666 discloses a conventional water pump including a substantially cylindrical pump housing including one end portion fixed on an outer portion of an engine block; a pulley rotatably supported through a ball bearing on an outer circumference of a supporting portion which is formed on the other end side of the pump housing, and which has a stepped portion formed so that a diameter is decreased, and connected through a belt with an output shaft of an engine; a shaft portion which is formed at a central portion of the pulley, which protrudes in the axial direction, and which is integrally formed with the pulley; and an impeller which is fixed on an end portion of the shaft portion, which is arranged to rotate as a unit with the shaft portion, and which is received in the inner circumference portion of the one end portion of the pump housing. The impeller is arranged to be rotated by the rotational driving force of the engine which is transmitted through the pulley to the shaft portion.
This water pump employs, as a ball bearing, a seal ball bearing having seal members arranged to liquid-tightly hold between an inner wheel and an outer wheel of the ball bearing, so as to keep a bearing ability of the ball bearing even when the water pump is exposed to the rainwater, the condensation, and so on. However, when a water with a dust is adhered to the seal member, the seal ability of the seal ball bearing may be deteriorated. In this water pump, the end surface of the stepped portion formed at the base end portion of the support member to which the inner wheel is fixed covers the seal member disposed at an end portion of the ball bearing which is on the engine side, and to which the water tends to adhered. With this, it is possible to improve the endurance of the seal member.